The present invention relates generally to hybrid electric vehicle systems and, more particularly, to variable engine shut off system for a hybrid electric vehicle.
Most of today""s motor vehicles carry an internal combustion engine that functions optimally at high speeds only. It is by necessity larger than an engine required for xe2x80x9cin townxe2x80x9d operation. Therefore a penalty is paid for the luxury of broad range operation, including the deterioration of our environment. Emissions during warm-up, low speed, and idle operations are not negligible. A large engine requires longer warm-up time, and short trips may not achieve warm-up in many cases, increasing the pollution problem
There exists, at the moment, much effort in addressing the basic need for an efficient power source at all operating conditions. One such effort, known as series hybrid electric, approaches the problem by carrying an on-board generator, which supplies electrical power to recharge batteries for an electric drive mechanism. This allows for xe2x80x9crange extendingxe2x80x9d at the cost of the additional weight of added components. In this scheme each of the power elements must be individually capable of the peak demands of the vehicle.
Another effort, known as parallel hybrid electric, holds a significant amount of promise. A parallel system allows the output from power components to be added together as required and therefore, each of the power components need only produce a portion of the power required of the series system components. Similarly, each of the power components is substantially lighter than its counterpart in the series hybrid. This reduction in weight also reduces power requirements, necessitating fewer batteries for the same range.
In most hybrid electric vehicle motors, an internal combustion engine is used to run the generator to produce electricity. If the exhaust emissions from the engine when it is operating are maintained at ultra low levels, the actual average emissions from the vehicle can be maintained close to zero since the engine will be shut off during idle, i.e., in city driving, the engine will shut off at every stop. The internal combustion engine can be operated inherently cleaner by being maintained at a constant speed and constant load, independent of the time-varying need for road horsepower. During most city driving it will not operate at idle, i.e., the hybrid electric vehicle will operate in an engine mode and the batteries will be charged continuously by the generator.
Along these lines, many hybrid electric vehicles are equipped with an engine shut off feature. The engine shut off occurs when a hybrid electric vehicle is stopped. This prevents hydrocarbon emissions generated when a normal vehicle is idling. This also helps improve overall fuel economy without intervention from the driver. In many existing systems, the engine shuts off after a predetermined pre-set time when the vehicle comes to a complete stop. To re-start the engine, the operator depresses the throttle pedal and clutch in manual transmission vehicle and releases the brake pedal in the automatic transmission vehicle. Unfortunately, customers in different regions and different countries prefer different engine shut off times.
The disadvantages associated with this conventional engine shut off technique have made it apparent that a new technique for engine shut off for a hybrid electric vehicle is needed. Preferably, the new technique would allow for a configurable shut off time. The new technique should also reduce hydrocarbon emissions generated when a vehicle is stopped while improving overall fuel economy.
It is an object of the invention to provide an improved and reliable means for engine shut off for a hybrid electric vehicle. Another object of the invention is to allow for a configurable shut off time. An additional object of the invention is to reduce hydrocarbon emissions generated when a vehicle is stopped while improving overall fuel economy.
In accordance with the objects of this invention, a engine shut off system for a hybrid electric vehicle is provided. In one aspect of the invention, an engine shut off system for a hybrid electric vehicle includes an internal combustion engine, an electric motor, and a controller. The internal combustion engine is located in the hybrid electric vehicle and is coupled to the electric motor. The vehicle system controller is coupled to the internal combustion engine and the motor, and may automatically shut off or start the internal combustion engine. When the hybrid electric vehicle is completely stopped the controller shuts the internal combustion engine off after a configurable period of time.
The present invention achieves an improved and reliable means for engine shut off for a hybrid electric vehicle. Also, the present invention is advantageous in that allows the time period before engine shut off occurs to be varied.
Additional advantages and features of the present invention will become apparent from the description that follows, and may be realized by means of the instrumentalities and combinations particularly pointed out in the appended claims, taken in conjunction with the accompanying drawings.